Efforts to alleviate the "heat island" effect are gathering momentum in Japan. Work is progressing on devices that lessen the tendency of cities to heat up more than other areas, such as rooftop greenery and water-retentive paving. Technology that keeps tall buildings cool and dry using natural wind, enabling reductions in the amount of heat given off by air conditioners, is also being developed. The government is taking action, too, setting up a commission among related ministries to formulate a comprehensive range of policies to tackle the heat-island phenomenon.

Cities Trap Heat
The heat-island effect refers to the phenomenon of localized higher temperatures in urban areas. Charts of temperature distribution over a wide area have revealed isolated "islands" of heat retained by cities, hence the name "heat island." Among the factors blamed for the phenomenon are the proliferation of buildings and other structures made of concrete, which retains heat; the blocking of wind paths; and increases in the amount of heat emitted by cars and air-conditioning systems.

The Ministry of the Environment issued a report on the heat-island phenomenon in August 2001. The report compared the number of hours for which the temperature in major cities was 30 degrees Celsius or more in 1980 and 2000. In Tokyo (35.4 degrees north latitude), for example, the number of 30-degree-plus hours rose dramatically, from 168 in 1980 to 357 in 2000. One of the consequences was that the number of people brought to hospital by ambulance with heatstroke almost tripled between the 1980s and the late 1990s. The phenomenon is also blamed for an increase in damage caused by localized heavy rain.

Work is progressing on the development of products and systems aimed at putting the brakes on urban warming. One example is technology that allows greenery to be planted on roofs and walls. By planting trees, flowers, and other plants on the roofs of buildings - shading the structures themselves from sunlight - it is possible to cut down on the electricity used for air conditioning, thus reducing the amount of heat released. Many general contractors have already commercialized systems that facilitate rooftop greenery.

Rooftop Greenery Spreading
When planting coniferous trees on roofs, Takenaka Corporation uses soil that is three times lighter than regular soil, enabling greenery to be installed without carrying out major structural reforms to the building in question. The company claims it can reduce the surface temperature of a roof by more than 10 degrees. Taisei Corporation, meanwhile, has brought out a product that makes it easy to cover building walls with greenery: A mat made of natural fiber is planted with ivy and attached - along with a sprinkling device - to the wall of the building. The firm has already received two large orders, including one for a building on which work will be started in October.

There are also moves to integrate anti-heat-island technology into buildings from the construction stage. Kajima Corporation is striving to develop technology for keeping high-rise buildings cool and free of humidity using natural wind. The technology will be employed in a 34-story building in Tokyo's Minato Ward that is due to be completed in 2003.

Water-Retentive Paving
Water-retentive paving has been developed that cuts the amount of heat reflected by roads, and the Tokyo metropolitan government has decided to use this paving in the redevelopment of vacant land at the former Shiodome Freight Terminal in Minato Ward. The surface of the road will absorb and retain water, reducing the surface temperature through the heat of vaporization. The new material is said to keep the road surface five to ten degrees cooler than regular paving.

At Tokyo University an experiment is being conducted to test a cooling method in which material known as a photocatalyst is used to make the walls of buildings retain water. At Tokyo University of Agriculture, meanwhile, practical tests are being conducted on using plants that can weather strong sunlight and wind and require little water - such as dandelions, other wild grasses, and coastal plants - for greenery on buildings.

The central government is set to establish a commission to consider policies to combat the heat-island effect. It will examine such measures as building cities so that wind from coastal areas can pass through them more easily, making it compulsory to set aside areas for greenery when constructing tall buildings, and reviewing transport systems to cut down on the heat emitted by vehicles.